The invention relates to a method and apparatus for the delivery of toner from a reservoir to a member carrying an electrostatic pattern to be toned before transfer to a receptor such as paper.
Toner in particulate form is normally supplied under gravity from an opening in the bottom of a hopper and transported from this opening to the point of transfer onto a charged member. A metering roll is typically used to measure selected amounts of toner from the hopper. It then transfers toner onto an applicator roll which then applies the toner to an electrostatic charge pattern defining the image to be printed. The problems associated with such systems have included the formation of lumps of toner at the bottom of the hopper and bridging across the bottom opening. Single component toners used in electrostatic printing tend to aggregate under pressure when stored in amounts sufficient to permit the printer to operate for an adequate period of time. This lumping and/or bridging results in an uneven distribution of toner and may interrupt printing entirely.
Toners commonly employed in electrographic printing are held on the surface of the applicator roll through magnetic forces. Iron oxide is incorporated into the toner formulation to obtain the magnetic properties required. This results in a toner that is expensive, dense and abrasive. Conductive toners are also used in printing. These toners contain carbon to provide suitable conductivity. However conductive toners can limit printing quality when colored toners are utilized.
In view of these considerations a system to provide a steady, evenly distributed flow of toner to the surface of a dielectric member is described.
Accordingly, it is an object of the invention to provide a system for delivering toner to a charged dielectric member. A related object is to provide an efficient and continuous delivery system for toner resulting in a printed image of desired quality upon transfer to paper. A further related object is to permit the use of non-magnetic, non-conductive toners.